The Waist–Hip Ratio is a Mediator Between Serum Levels of Brain-Derived Neurotrophic Factor and Its Val66Met Polymorphism in Adolescents

Figures & data

Table 1 Anthropometric, Biochemical, and Dietary Characteristics of the Adolescents

Variables	Total (N = 644)	Male Adolescents (N = 278)	Female Adolescents (N = 366)	p*
Serum BDNF (ng/mL)	56.30 ± 28.13	55.17 ± 25.96	57.16 ± 29.68	0.375
Ages (years)	16.87 ± 0.59	16.96 ± 0.60	16.80 ± 0.57	<0.001
BMI (kg/m^2)	20.31 ± 2.36	19.83 ± 2.35	20.67 ± 2.30	<0.001
WHR	0.78 ± 0.05	0.77 ± 0.04	0.78 ± 0.05	0.015
Heart rate (beats/min)	82.74 ± 11.26	79.90 ± 10.88	84.90 ± 11.08	<0.001
SBP (mmHg)	118.9 ± 11.70	121.1 ± 12.30	117.2 ± 11.00	<0.001
DBP (mmHg)	72.87 ± 10.49	73.30 ± 10.35	72.55 ± 10.60	0.367
TC (mmol/L)	3.59 ± 0.58	3.43 ± 0.52	3.72 ± 0.59	<0.001
HDL-C (mmol/L)	1.41 ± 0.28	1.36 ± 0.27	1.45 ± 0.28	<0.001
TG (mmol/L)	1.13 ± 0.44	0.96 ± 0.35	1.25 ± 0.46	<0.001
LDL-C (mmol/L)	1.67 ± 0.49	1.63 ± 0.48	1.70 ± 0.51	0.066
Glucose (mmol/L)	5.06 ± 0.44	5.13 ± 0.44	5.01 ± 0.43	<0.001
Insulin (μIU/mL)	12.06 ± 5.64	9.72 ± 4.52	13.83 ± 5.77	<0.001
Vitamin A intake (μg/day)	369.6 ± 795.9	455.4 ± 1061	304.5 ± 501.9	0.029
Thiamine intake (mg/day)	1.56 ± 1.00	1.84 ± 1.24	1.34 ± 0.71	<0.001
Riboflavin intake (mg/day)	0.70 ± 0.53	0.82 ± 0.72	0.60 ± 0.29	<0.001
Vitamin B6 intake (mg/day)	0.40 ± 0.25	0.42 ± 0.27	0.39 ± 0.23	0.276
Folic acid intake (μg/day)	83.7 ± 63.07	90.17 ± 69.13	78.79 ± 57.67	0.027
Niacin intake (mg/day)	14.44 ± 11.07	17.63 ± 14.80	12.02 ± 60	<0.001
Vitamin C intake (mg/day)	60.1 ± 59.43	62.25 ± 77.15	58.47 ± 41.23	0.460
Vitamin E intake (mg/day)	27.73 ± 19.25	27.28 ± 23.18	28.08 ± 15.64	0.623
Calcium intake (mg/day)	372.0 ± 367.6	432.2 ± 471.1	326.3 ± 254.6	0.001
Phosphorus intake (mg/day)	990.9 ± 564.4	1149 ± 701.5	870.9 ± 392.7	<0.001
Potassium intake (mg/day)	1838 ± 1401	2061 ± 1797	1669 ± 971	0.001
Sodium intake (mg/day)	3272 ± 2505	3594 ± 3277	3028 ± 1663	0.009
Magnesium intake (mg/day)	308.3 ± 209.8	350.8 ± 272.5	276.0 ± 136.9	<0.001
Iron intake (mg/day)	20.56 ± 16.36	22.3 ± 19.5	19.24 ± 13.37	0.025
Zinc intake (mg/day)	8.86 ± 6.10	10.34 ± 8.05	7.73 ± 3.67	<0.001
Selenium intake (μg/day)	50.71 ± 58.29	55.98 ± 62.29	46.70 ± 54.81	0.045
Copper intake (mg/day)	1.80 ± 1.44	2.04 ± 1.80	1.62 ± 1.06	0.001
Manganese intake (mg/day)	7.47 ± 20.98	9.46 ± 26.41	5.95 ± 15.53	0.049
Iodine intake (μg/day)	5.97 ± 13.32	8.17 ± 15.39	4.29 ± 11.25	<0.001
Protein intake (g/day)	81.95 ± 54.54	98.74 ± 70.29	69.2 ± 33.36	<0.001
Fat intake (g/day)	98.58 ± 67.84	119.3 ± 85.40	82.86 ± 44.64	<0.001
Carbohydrate intake (g/day)	373.1 ± 182.7	406.8 ± 214.3	347.4 ± 149.8	<0.001
Dietary fiber intake (g/day)	18.86 ± 16.93	19.97 ± 19.86	18.02 ± 14.29	0.167

Note: *Male adolescents vs female adolescents by t-tests.

Table 2 Allele and Genotype Frequencies of Bdnf Val66Met in the Study Population

		Total (N = 644)	Hardy–Weinberg p	Male Adolescents (N = 278)	Female Adolescents (N = 366)	p*
Genotypes	Val/Val	175 (27.3)	0.954	79 (28.7)	96 (26.2)	0.832
	Val/Met	327 (50.7)		139 (49.8)	188 (51.4)
	Met/Met	142 (22.0)		60 (21.5)	82 (22.4)
Alleles	Val	677 (52.6)	–	297 (53.6)	380 (51.9)	0.612
	Met	611 (47.4)		259 (46.4)	352 (48.1)

Notes: Data are expressed as n (%). *Male adolescents vs female adolescents by Fisher’s exact tests.

Figure 1 Serum BDNF levels in the subjects with different genotypes of Bdnf Val66Met. **p<0.01; ns, p>0.05.

Table 3 Factors Associated with Serum BDNF Levels in the Adolescent Population (N = 644)

Variables	Adjusted R^2 = 0.069
	β	Partial Correlations	p
WHR	−0.163	−0.165	<0.001
Iodine intake	0.132	0.136	0.001
Heart rate	0.108	0.111	0.005
HDL-C	0.098	0.101	0.011
Dietary fiber intake	0.082	0.084	0.033

Abbreviation: β, standardized regression coefficient.

Table 4 Factors Associated with Bdnf Val66Met in the Adolescent Population (N = 644)

Variables	Adjusted R^2 = 0.015
	β	Partial Correlations	p
SBP	0.097	0.098	0.013
WHR	0.091	0.091	0.021

Note: 1 = Val/Val, 2 = Val/Met and 3 = Met/Met genotype of Bdnf Val66Met.

Abbreviation: β, standardized regression coefficient.

Table 5 Hypothesized Mediation Model of WHR Between Bdnf Val66Met and Serum BDNF Levels

	Effect	SE	Boot LLCI	Boot ULCI	Proportion
Total	−4.413	1.576	−7.507	−1.319	100%
Direct	−3.837	1.563	−6.907	−0.767	86.95%
Indirect	−0.576	0.278	−1.161	−0.087	13.05%

Abbreviations: Effect, regression coefficient; SE, standard error; Boot LLCI, bootstrapping lower limit confidence interval; Boot ULCI, bootstrapping upper limit confidence interval; Direct, direct effect of Bdnf Val66Met on serum BDNF levels; Indirect, indirect effect of Bdnf Val66Met on serum BDNF levels through WHR; Total, the sum of direct and indirect effect.

Figure 2 Mediation model for serum BDNF levels, Bdnf Val66Met and WHR. (A) Path diagram for the regression model. (B) The simple mediation model with WHR as a mediator of the effect of Bdnf Val66Met on serum BDNF levels.

Notes: Path coefficients were shown in standardized regression coefficient. *p < 0.05; **p < 0.01; ***p < 0.001.